In nations where importance is attached to diesel engine automobiles, it is necessary to clear a strict exhaust gas regulation. Thus, various catalyst apparatuses have been developed for decreasing exhaust gases from a diesel engine. Of these catalyst apparatuses, urea selective reduction systems are recommended as apparatuses for reducing NOx to be clarified into nitrogen and water in the range of temperatures at which the speed of their engine is low (Non-Patent Literature 1).
Moreover, suggested is a method of mixing a NOx reducing catalyst, an oxidizing catalyst for hydrocarbons, and an ion electroconductive solid electrolyte with each other and then arranging the mixture to be dispersed on the surface of a metallic honeycomb, thereby decomposing NOx electrochemically (Patent Literature 1). In this invention, as the metallic honeycomb, supplied is a honeycomb structure or a stacked structure similar thereto that is obtained by stacking a stainless steel waved plate, which is worked into a wave form, and a stainless steel flat plate onto each other (Patent Literature 2, and Non-Patent Literature 2).
Suggested is also a method of applying a voltage of an anode and a cathode between which a solid electrolyte (SE) layer in order to promote the decomposition of NOx by electrochemical reaction (Patent Literature 3).